Okay, so I have a 16 gallon with a filter and a heater. I got a 100 watt heater from Petco (their brand) and it's awful. It doesn't have a temp indicator so I'm working on guesswork. I want to replace it and I'm looking for a decent submersible that you guys have had good experience with. Also, I'm thinking of going down to 50 watts. This heater is always running higher then it should. Right now I have it at 78 but it will probably creep up to 80 by morning. It's driving me bonkers. Any suggestions on a good heater?

i too would recommend a visi-therm stealth heater. it's a little more pricey compared to the other submersibles but the quality is well worth the investment. it is suggested 5 Watt for every gallon but i chose to use a 100 Watt for my 10 gallon. because your tank is bigger, i would go for a 150 Watt.